In ancient times, an
aztec warlord named Yaotl opens a portal into a
parallel universe that grants him immortality and petrifies his four generals. The portal also releases thirteen immortal monsters that destroy his army and his enemies while becoming famous mythical monsters as centuries pass. In the present, the Teenage Mutant Ninja Turtles grow apart after defeating
the Shredder. For training,
Master Splinter sends
Leonardo to
Central America, where he becomes the protector of a village, to which the villagers refer to him as the "Ghost of the Jungle".
Donatello works as an
IT specialist,
Michelangelo works as a birthday party entertainer named "Cowabunga Carl", and
Raphael continues to fight crime as a masked
vigilante known as the "Nightwatcher", which he keeps a secret. The Turtles' old friend
April O'Neil now operates a shipping company that acquires relics for collectors, assisted by her boyfriend,
Casey Jones. After traveling to Central America for work, April tells Leo his brothers have drifted apart. She then returns to
New York City with a statue for wealthy tycoon Max Winters. Winters hires Shredder's former second-in-command,
Karai and her ninja
Foot Clan to search the city for the thirteen monsters before the portal opens again. Casey figures out Raph's double identity and joins him in hunting criminals. Winters, who is actually Yaotl, reanimates his four stone generals using technology created by his company. Leo returns to the Turtles' lair, where Splinter forbids crime-fighting until they can work as a team. During training, they disobey Splinter and engage
Bigfoot, one of thirteen beasts, clashing with the Foot Clan in the process. Bigfoot is ultimately captured by Yaotl's generals. Splinter scolds the Turtles the next day as the Foot and generals capture more monsters. Later, Raphael and Casey encounter the Vampire Succubor but are spotted during its capture. Despite escaping, Raph is knocked unconscious. Casey and April care for him and alert the others, leading to the discovery of Yaotl's identity. Revived, Raph urges action, but Leo insists on Splinter's permission. Frustrated, Raph decides to investigate alone. Donnie learns the next portal will open at Winters' tower, and Splinter urges Leonardo to find Raphael. Yaotl reveals his plan to break the curse and restore his generals to humanity, but the generals plot to betray him and remain immortal. As the Nightwatcher, Raph battles the
Jersey Devil and drives it off. Mistaking Raph for a thug, Leo pursues him, leading to a fight where Leo learns Nightwatcher is his brother. Raph nearly kills Leo in anger but flees in guilt. The generals capture the weakened Leo to replace the thirteenth beast, prompting a remorseful Raph to rescue him. As the portal opens, Yaotl discovers his generals' betrayal. Splinter, the Turtles, Casey, and April fight through the Foot Clan to reach the tower and uncover Yaotl's true intentions. Refusing to betray Yaotl, Karai and the Foot Clan join forces with April and Casey to locate the final monster, the
Sea Monster, while the Turtles battle the generals. Splinter and Yaotl fend off monsters emerging from the portal. April, Casey, and Karai bring the Sea Monster to the tower, where it collides with the generals. Yaotl saves the Turtles, dragging the generals into the portal and turning them human before it closes. Karai warns the Turtles to savor their victory, hinting at the Shredder's return, before vanishing. A mortal Yaotl thanks the heroes and fades into the afterlife. His helmet joins Splinter's trophy collection alongside Raph's Nightwatcher helmet and Mikey's Cowabunga Carl mask. Returning to their roles as New York's protectors, Raph reaffirms that the Turtles will always be brothers. ==Voice cast==